KR102650098B1 - Array-based free-space optical communication links - Google Patents

Abstract

Optical communication with a remote node includes transmitting at least one optical beam to the remote node; receiving at least a portion of at least one optical beam from a remote node; providing intensity information based on one or more signals from one or more optical detector modules in an array of optical detector modules that detect a portion of an optical beam received from a remote node; and controlling at least one optical phased array to steer an optical beam transmitted to the remote node based on intensity information received from the remote node.

Description

Array-based free-space optical communication links

Cross-reference to related application(s)

This application claims the priority and benefit of U.S. Provisional Patent Application No. 62/935,471, entitled “Array Based Free Space Optical Communication Links,” filed on November 14, 2019.

technology field

This disclosure relates to array-based free-space optical communication links.

Some free-space optical (FSO) communication links operate with optical elements arranged for point-to-point communication. For example, two nodes communicating with each other through a point-to-point communication link may each have relatively large lenses to direct the optical beams from the transmit aperture of one node to the receive aperture of another node. Each telescope arrangement can be used, including: These FSO communication links are potentially sensitive to disturbances such as misalignment, vibration and scintillation.

In one aspect, generally, an apparatus for optical communication with a remote node includes: a receiver module configured to receive at least a portion of at least one optical beam from a remote node, the receiver module comprising: at least one array of optical detector modules; and circuitry configured to control the optical detector modules and provide intensity information based on one or more signals from one or more of the optical detector modules; and a transmitter module configured to transmit at least one optical beam to the remote node, the transmitter module comprising: at least one optical phased array providing an optical beam transmitted to the remote node, and steering the optical beam transmitted to the remote node. ), comprising circuitry configured to receive intensity information from a remote node to control the optical phased array.

In another aspect, generally, a method for optical communication with a remote node includes: transmitting at least one optical beam to the remote node; Receiving at least a portion of at least one optical beam from a remote node; providing intensity information based on one or more signals from one or more optical detector modules in an array of optical detector modules that detect a portion of an optical beam received from a remote node; and controlling at least one optical phased array to steer an optical beam transmitted to the remote node based on intensity information received from the remote node.

Aspects may include one or more of the following features.

The array of optical detector modules includes a two-dimensional array of photodiodes each providing a respective photocurrent to a corresponding amplifier.

The photodiodes include avalanche photodiodes and the amplifiers include transimpedance amplifiers.

The circuitry of the receiver module is configured to determine a subset of less than all amplifiers to be powered on based at least in part on comparing the photocurrent in the corresponding amplifier to a threshold.

Circuitry of the receiver module is configured to determine a first subset of photodiodes that are receiving at least a portion of an optical beam and a second subset of photodiodes that are receiving at least a portion of another optical beam.

The receiver module further includes a light source that provides a coherent local oscillator beam for coherently receiving the optical beam.

The light source provides multiple coherent local oscillator beams for coherently receiving multiple optical beams simultaneously.

The intensity information from the remote node is received by circuitry of the transmitter module via a side-channel network separate from the free space optical communication link with the remote node, at least during setup of the free space optical communication link.

Additional intensity information from the remote node is received by circuitry in the transmitter module for controlling the optical phased array via the free space optical communication link after setup of the free space optical communication link.

The receiver module further includes an array of microlens adjacent to the array of optical detector modules.

The receiver module further includes at least one lens configured to focus light proximate to the microlens array.

The distance between the microlens array and the lens is at least 5% larger or smaller than the focal length of the lens.

The receiver module further includes at least one lens configured to focus light proximate to the array of optical detector modules.

The distance between the array of optical detector modules and the lens is at least 5% larger or smaller than the focal length of the lens.

The array of optical detector modules includes an array of photodetectors within a photonic integrated circuit.

The optical phased array includes a two-dimensional array of optical emitters each coupled to a respective optical phase shifter, each phase shift signal applied to the optical phase shifter being an optical beam transmitted to a remote node at least in a first plane. Controls the steering of the propagation axis.

Respective phase shift signals applied to the optical phase shifters control steering of the propagation axis of the optical beam transmitted to the remote node in a second plane perpendicular to the first plane.

Tuning the wavelength of the optical waves emitted from the optical emitters controls the steering of the propagation axis of the optical beam transmitted to the remote node in a second plane perpendicular to the first plane.

Aspects may have one or more of the following advantages.

In some implementations of the communication system described herein, a transmitter module can dynamically steer light from a transmit aperture, and a receiver module can recover data communicated over the link and intensity information used for dynamic steering. To do this, light from the receiving aperture can be collected. In some implementations, the transmitter module uses an optical phased array (OPA) (e.g., an OPA integrated on an optical chip) for dynamic steering, and the receiver module uses a high-speed detector array system. Such dynamic alignment may be useful in providing high-speed optical communication systems that are less sensitive to some of the potential disturbances such as misalignment, vibration, and scintillation, for example. In some implementations, portions of the system may be mounted on mobile transmitter (Tx) and receiver (Rx) platforms, which may further facilitate dynamic alignment of the system.

Other features and advantages will become apparent from the following description and from the drawings and claims.

The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, various features of the drawings are not to scale. Conversely, the dimensions of various features are arbitrarily enlarged or reduced for clarity.
1A is a schematic diagram of an example communication system.
Figures 1B-1E are schematic diagrams of alternative communication nodes.
Figure 2 is a schematic diagram of an example beam steering arrangement.
3A and 3B are schematic diagrams of examples of beam steering arrangements.
4A and 4B are schematic diagrams of a side view and a top view, respectively, of a microlens-emitter array.
Figure 5 is a schematic diagram of the optical geometry for the lens.
Figure 6 is a schematic diagram of an optical receiving arrangement.
Figure 7 is a schematic diagram of an optical receiving arrangement.
Figure 8 is a schematic diagram of an optical receiving arrangement.
Figure 9 is a schematic diagram of an optical receiving arrangement.
Figure 10 is a schematic diagram of an optical receiving arrangement.
Figures 11A and 11B are schematic diagrams of optical receiving arrangements.
Figure 12 is an example of received intensity patterns on a detector array.
Figure 13 is a schematic diagram of a multi-beam FSO communication system.
14A-14D are schematic diagrams of mesh network configurations.
15A and 15B are schematic diagrams of coherent detection configurations.
Figure 16 is a schematic diagram of a coherent detection configuration.
Figure 17 is a schematic diagram of a multi-channel coherent FSO communication system.
Figure 18 is a schematic diagram of an exemplary detection arrangement.
Figure 19 is a circuit diagram of an exemplary readout circuit.
Figure 20 is a schematic diagram of an exemplary detector module geometry.
21 is a schematic diagram of exemplary detector module circuitry.
Figure 22 is an illustration of an exemplary detector array arrangement.
Figure 23 is a schematic diagram of an exemplary detector array arrangement.
Figure 24 is a schematic diagram of examples of optical intensity patterns for different received beams.
25 is a schematic diagram of an exemplary FSO communication system.
26 is a schematic diagram of an example arrangement for dynamic beam steering.
27A and 27B are schematic diagrams of example detection arrangements.

1A , an example communication system is configured to communicate over a high-speed FSO two-way communication link (or simply “FSO link”) using optical beams transmitted in both directions between communication nodes 100A and 100B. It includes a local node (100A) and a remote node (100B). As described in more detail below, there is also a side-channel two-way communication link (or simply a “side-channel link”) used in some implementations for initial alignment and/or ongoing dynamic alignment. The side-channel link need not be particularly fast (e.g., an order of magnitude slower or more than an FSO link), but may provide relatively low latency. For example, side-channel network 101 may be any of a variety of types of networks, including a point-to-point network dedicated to nodes 100A and 100B, and may be connected to wired media (e.g. , coaxial cable), wireless media such as radio frequency (RF) links, and/or optical media (e.g., optical fiber).

In this example, local node 100A provides an outgoing beam 102A that can be steered over a solid angle in the direction of remote node 100B and an incoming beam 104A. ) is configured to receive. Beam steerer 106 may be configured to use any of a variety of techniques to steer the emission beam 102A, including optical phased arrays, as described in more detail below. . Local node 100A is also configured to modulate data from incident data stream 108 onto emitting beam 102A. Incident intensity feedback port 110 provides intensity information transmitted by remote node 102B via side-channel network 101, which is used by beam steerer 106 to steer emission beam 102A. do. Local node 100A also includes a detector array 112 that includes a distribution of closely spaced optical detector modules with detected signals representing individual pixels of the detection area. Detector array 112, beam steerer 106, and other components within node 100A may be supported on a platform or other rigid structure, for example. In some implementations, remote node 100B includes the same components as local node 100A. Although some configuration and alignment procedures will be described in the context of local node 100A, substantially the same procedures may also be performed at remote node 100B.

Typically, incident beam 104A has an incident optical intensity profile that is spread out over multiple pixels. Local node 102A includes circuitry configured to control the optical detector modules of detector array 112 and provide intensity information from emission intensity feedback port 116 for transmission to remote node 100B. Signals based on intensity information from optical detector modules at one node may be due to atmospheric effects (e.g., intensity scintillation due to air turbulence between nodes) and/or movement of one or both nodes. It can be transmitted to other nodes to guide dynamic steering of the beams to compensate for drift in the intensity profile across pixels. Power can also be saved by controlling which optical detector modules are simultaneously active during detection. For example, the optical detector module may include a two-dimensional array of photodiodes (e.g., avalanche photodiodes) each providing a respective photocurrent to a corresponding amplifier (e.g., transimpedance amplifier). there is. The amplifier can be turned on or off appropriately to save power based on whether the output of the photodiode exceeds a threshold.

When the FSO link between nodes 100A and 100B is initially set up, there is an initial alignment procedure that includes a rough alignment phase and a fine alignment phase. During the coarse alignment phase, the emitting beam 102A is aimed in a general direction that is assumed to be directed to the remote node 100B according to predetermined position information (e.g., GPS coordinates or other absolute or relative coordinates). do. The coarse alignment phase also optionally includes coarse steering using information from telescopes at local node 100A and/or from retroreflectors on or near remote node 100B. can do. Coarse alignment phase may not be necessary for some communication sessions, for example, if emission beam 102A is already roughly aligned from a previous FSO link used between nodes 100A and 100B. .

When emission beam 102A reaches remote node 100B as incident beam 104B, fine alignment phase is required to ensure that incident beam 104B is properly positioned relative to the detector array of remote node 100B. can be used In some cases, incident beam 104B may represent only a portion of the power from emitted beam 104A, for example, due to absorption or other disturbances from atmospheric propagation or due to beam divergence. As part of the fine alignment phase, intensity information may be captured at remote node 100B and provided to intensity feedback port 110 via side-channel network 101. The intensity information may include a signal quality measurement that indicates how much power in incident beam 104B is being detected by optical detector modules within the detector array of remote node 100B.

After the FSO link is operational, there may also be an on-going dynamic alignment used to continue steering the emission beam 102A based on intensity information used as feedback from the remote node 100B. For example, the steering may need to be adjusted to change atmospheric conditions that affect the direction of propagation of the beam. In some implementations, after the FSO link is operational, instead of transmitting intensity information using the side-channel network 101 between nodes for dynamic alignment of beams in both directions, the intensity information is transmitted in both directions. may be transmitted as information embedded within data communication streams (e.g., using time domain or frequency domain multiplexing).

1B-1E show examples of alternative implementations of a communication node. 1B, node 100C includes a lens 120, or other beam shaping optical elements, to limit beam divergence and ensure that the incident beam at the remote node remains relatively well focused. do. Referring to FIG. 1C , node 100D includes a lens 122, or other beam shaping optical elements, to collect light across the lens aperture and direct at least a portion of incident beam 104A to detector array 112. Focus on a portion of (e.g., one or a relatively small number of pixels). In the example of Figure 1D, node 100E includes both transmitter-side lens 120 and receiver-side lens 122. For node 100C without a transmitter-side lens, a larger field of view may be achieved in some implementations. For node 100B without a receiver-side lens, lower sensitivity to alignment errors may be achieved in some implementations.

Referring to Figure 1E, detector array 112 may be placed at a distance that does not exactly coincide with the focal plane associated with receiver-side lens 122. For example, for a substantially collimated optical beam (e.g., for propagation over relatively long distances), the densest spot size after the receiver-side lens 122 is that of the lens 122. It will be close to the focal length. Placing detector array 112 at a distance greater than (or closer to) the focal length will result in a beam that is not perfectly focused on detector array 112, as explained in more detail below: This may be beneficial in some implementations. The amount of defocus may vary, but in some implementations, the distance between lens 122 and detector array 112 is at least about 5% greater or less than the focal length, or at least about 10% greater or less.

2, an example beam steering arrangement 200 provides data from an incident data stream (e.g., into binary data symbols mapped to different intensity levels) (e.g., intensity modulation). and a tunable laser 202 that can be modulated using . The light is then distributed by a network of splitters 204 to an array of phase shifters 206 and an array of optical emitters 208. This optical phased array can be steered in two angular dimensions using wavelength and phase. Tunable laser 202 can have its wavelength (or equivalently, its frequency) tuned to steer across one angular dimension of the solid angle, and phase shifters 206 can steer across another angular dimension of the solid angle. You can have their relative phase shifts tuned to steer.

Referring to Figures 3A and 3B, other examples of beam steering arrangements use a two-dimensional optical phased array that can be steered using phase over both angular dimensions. 3A shows an array 300A comprising optical emitters 302 distributed over a rectangular shaped area, where light is distributed to phase shifters 304 coupled to each of the emitters 302. . In this example, light is delivered to emitters 302 using an “H-tree” shaped splitter network. This phase control can also be performed in a sub-phase array format allowing for fewer input/output (I/O) controls, as described in more detail in U.S. Pat. No. 10,613,410, which is incorporated herein by reference. .

A potential issue that may be encountered in array 300A is that emitters 302 may have a spacing from their nearest neighbors greater than a certain sub-wavelength pitch (e.g., half the operating wavelength), which This will result in side lobes in the array emission pattern. One way to mitigate the effect of the side lobes (eg, reduce the amount of power radiated into the side lobes) is to make the component factor associated with the individual emitters more directional. For example, FIG. 3B shows that individual emitters can be further separated by positioning the microlens array 306 in close proximity to the emitters 302 such that the lenses within the microlens array 306 are spaced at approximately similar pitch as the emitters 302. One method of making it directional is shown. In some implementations, the centers of the lenses can be fine-tuned to substantially match the positions of the emitters.

Figure 4 shows in side view an example of a microlens 400 that may be placed over an optical emitter 402. In this example, the microlens 400 is formed in a glass substrate with a refractive index of 1.44, and has a diameter of about 95 μm, a radius of curvature of about 120 μm, and a numerical aperture (NA) of about 0.2. There is a working distance of approximately 240 μm between the microlens 400 and the silicon waveguide emitter 404. The emitter 404 may be implemented as a waveguide with a grating structure embedded in an oxide cladding 406 over a silicon substrate 408 fabricated using a silicon-on-insulator (SOI) platform. . FIG. 4B shows a top view of an array 410 of microlenses 400 within a microlens array, disposed over respective optical emitters 402.

5 shows an example of a lens 500 and the resulting optical geometry used as a microlens in a microlens array related to making the emission/collection device more directional to provide side-mode suppression. It shows. In this example, lens 500 is assumed to have a focal length of approximately 200 μm, and the resulting focused spot size in the focal plane is approximately 8 μm. The observation viewing angle is approximately 1.5 degrees. As the size of the lens (and resulting numerical aperture) increases, directivity increases.

Referring to Figure 6, the inclusion of a receiver-side lens in an optical receiving array may reduce the field of view (or "field of regard"), for example, if only one receiver (e.g., photodetector) is used. "or "collection cone"). However, the field of view can be increased with a receiver-side lens 600 using multiple receivers appropriately arranged over the focal surface. When the direction of the incident plane wave changes (e.g., from incident beam 602A to incident beam 602B), the focusing point of the corresponding receiver changes on the hemispherical focal surface (e.g., from receiver 602A to receiver Go to (602B). A hemispherical arrangement of these receivers will allow light to be received over a relatively large cone of space. Alternatively, if there is only a single receiver placed at the center of the lens axis, the light will be received from a more confined cone of space.

Figures 7 and 8 show different optical receiving arrangements without and with a receiver-side lens, respectively. Referring to FIG. 7 , when there is no receiver-side lens in the receiving array, photodetector 700 has a viewing field of view 702 that depends on the acceptance angle and refractive index of photodetector 700. Referring to Figure 8, when there is a lens 800 within the receiving array, the secondary factor further limits the array to a narrower field of view 802. In particular, as described above, there is an associated movement of focus on the focal surface 804 relative to the lens 800 when the angle of the incident beam changes. 9 shows an array of multiple photodetectors disposed on a lens 900 and a hemispherical focal surface 902, capable of receiving focused spots from different incident beams 904A and 904B arriving at different angles. The optical receiving arrangement is shown. For example, the position and/or angle of the incident beam may drift due to the effects of atmospheric propagation. Electrical signals 906 from different photodetectors correspond to different pixels with different intensities in the received images, which can change during operation of the FSO link as the beam drifts.

10, in some light receiving arrangements, the lens coupling system 1000 is arranged to receive incident beams arriving from different angles (e.g., incident beam 1002A or incident beam 1002B). It includes multiple lenses having different shapes and/or focal lengths, or multiple components of a composite lens. As an alternative to the hemispherical focal surface associated with a single lens, the lens combination system 1000 can provide a flattened focal surface that more closely matches the desired flattened detection surface 1004. In some implementations of the detector array, the flattened focal plane 1004 may be a more suitable arrangement for distributing the photodetector and/or other components of the detector modules of the detector array. In such an optical receiving arrangement, the beam received via the off-center incidence path may be intentionally defocused at certain portions of the detection surface 1004, as shown at the slightly defocused edge location 1006. You can.

The optical receiving arrangements of FIGS. 11A and 11B further illustrate how intentional defocusing can have positive results in some implementations. Referring to FIG. 11A , lens system 1102 (e.g., a system of one or more lenses) corresponds to different photodetectors in photodetector array 1104 and different microlenses in microlens array 1106. Each focus spot for different pixels maps to different incident reception angles and positions within the field of view 1108. In this example, where the spot sizes are relatively dense (approximately a single pixel width), the light is collected very efficiently for some reception angles/positions. For example, incident beam 1110A is focused on one of the pixels to produce electrical signal output 1112A from that pixel. However, there are gaps in the field of view 1108 at other angles/positions, where light falls between pixels and produces little or no electrical signal (i.e., is not received).

Gaps in acceptance angles/positions can be reduced or eliminated by having a spot size larger than the pixel size and/or by having a small amount of defocus in the beam collected by the microlens array 1106. Referring to Figure 11B, field of view 1114 includes overlapping cones of accommodation angles, each mapping to multiple pixels. For example, incident beam 110B is focused on a number of pixels 1116B to generate electrical signal outputs 1112B from those pixels 1116B. The effect of defocusing can also be seen in the example of Figure 12, where focused intensity patterns are shown on pixels of a 21x21 pixel detector array 1200 with a pixel size of approximately 200 μm. This example shows intensity patterns for two different possible beam trajectories of a beam transmitted from a square-shaped transmitter-side aperture. Alternatively, two different intensity patterns may correspond to multiple beams received simultaneously, as described in more detail below. In this example, the square shape of the transmitter-side aperture and the finite emitter spacing of the transmitter-side OPA have a central main lobe covering more than one pixel, and a number of sides along two orthogonal dimensions on either side of the main lobe. This resulted in an intensity pattern for each focal spot, with lobes.

If electrical signal outputs from multiple individual pixels are collected simultaneously, more than one data stream may be received simultaneously from one detector array. Figure 13 shows a multi-beam FSO communication system in which four communication nodes 1300A, 1300B, 1300C, and 1300D are configured to communicate with each other. Node 1300A receives beams from multiple nodes 1300B and 1300C simultaneously in this example. In general, any number of communication nodes can be arranged to communicate in a mesh network where each communication node can be transmitting and receiving data from any other communication node. In this example, each communication node has a single transmitter-side port, but simultaneously has multiple receiver-side ports corresponding to multiple intensity patterns that can be detected on the detector array. Accordingly, various mesh network configurations are possible, as shown in Figures 14A-14D, where arrows indicate transmission of data over the FSO link between different communication nodes (represented by circles). In other examples, each communication node includes multiple transmitter-side ports, for example, by transmitting multiple beams from multiple transmitter-side apertures, potentially leading to more complex and flexible mesh network configurations. can do.

Other possible features that may be included in some implementations of a communication system using FSO links described herein include modulation techniques other than intensity modulation using binary bits. For example, if the receiver circuit includes linear amplifiers and nonbinary decision circuits, it is possible to transmit more information using PAM4 or higher-order amplitude modulation. Additionally, if a coherent local oscillator (LO) (e.g. light from a laser) is used, it is possible to use coherent detection with phase modulation. Using coherent detection techniques can complicate the receiver circuitry, but can also significantly increase the sensitivity of the system for long-distance communication links where very few photons can reach the receiver. 15A illustrates a uniform illumination system in which a receiver-side lens 1502 focuses incident light onto a detector array 1504 and an LO laser 1506 and lens 1508 are used to uniformly illuminate the detector array 1504. An example of configuration 1500A is shown. In some implementations, an initial uniform illumination configuration 1500A is initially used to localize the signal from the beam, and then a directed illumination configuration 1500B is used to more tightly focus and steer the signal as part of the detector array 1504. Used with LO beam. For example, LO control system 1510 can include a fast feedback loop to control LO spot size and dynamically steer the LO beam. The LO laser 1506 can be locked to the transmit laser at the remote node, and the hybrid receive circuit can extract the phase of the modulated light. FIG. 16 shows an example coherent detection configuration 1600 that includes a receiver-side lens 1602 to focus light from multiple received beams onto a detector array 1604. In this example, there are multiple LO sources 1606A and 1606B to provide a separate coherent LO beam to simultaneously interfere with each of two different received beams. In this way, any number of independent LO sources can be used to implement a multi-channel receiver.

Figure 17 shows an example configuration of a multi-channel coherent FSO communication system 1700. There is a node 1702 containing Tx Laser 1 and a node 1704 containing Tx Laser 2, which provide modulated optical waves with respective data streams (Data 1 and Data 2). These optical waves are emitted as separate optical beams that propagate through the atmosphere 1706 and are received by node 1708. In this example, light collection is shown for two detector modules in an array of multiple detector modules. Laser LO1 and laser LO2 provide separate LO beams directed to individual detector modules for detection of the in-phase and quadrature-phase (I/Q) components of the coherently detected signal, which generates data streams. It is provided to a digital signal processing (DSP) circuit for demodulating 1 and data 2).

미만의 잡음)에 의해 증폭되고, 제한 증폭기에 공급되고, 디지털화될 수 있는 전압 신호 출력을 제공할 수 있다. 도 19는 판독 회로(1900)의 하나의 가능한 구현을 도시한다. 도 20은 개별 픽셀에 대한 예시적인 치수들을 갖는 예시적인 검출기 모듈(2000)을 도시한다. 약 36 내지 75㎛ 직경의 활성 영역을 갖는 APD가 존재한다. 약 50 내지 200㎛ 직경의 영역을 갖는 APD 주위의 관련된 회로부의 배열이 존재한다. 약 4㎠의 전체 검출기 영역 내의 픽셀들의 총 수는, 예를 들어, 약 10,000 내지 160,000일 수 있거나, 수백만 개의 픽셀들이 존재할 수 있는 더 큰 검출기 영역을 갖는다.In implementations where there is a relatively large number of detector modules in the system, it is desirable to be able to process the received data streams and read out the incident data without introducing excessive noise, parasitics, and/or loss in potentially weak signals. useful. 18 shows a receiver-side lens arranged in front of a detector array 1806 of detector modules each including readout circuitry on an integrated SiGe BiCMOS platform providing a transimpedance amplifier (TIA) for each detector module. 1802) and a microlens array 1804. When a TIA is placed directly below a corresponding avalanche photodiode (APD) photodetector, the APD provides an initial gain (e.g., between about 10 and 1000) and directs the resulting photocurrent to the TIA gain stage. can be supplied. TIA power consumption is relatively low (e.g., less than about 1 mW per pixel for TIA amplification from 1 μA to 0.8 Vpp). A low-noise TIA with a bandwidth appropriate for the data rate can be used with a low-noise amplifier (e.g., about 3㎀/

It can be amplified (less than noise), fed to a limiting amplifier, and provide a voltage signal output that can be digitized. 19 shows one possible implementation of readout circuit 1900. Figure 20 shows an example detector module 2000 with example dimensions for individual pixels. There are APDs with active regions of about 36 to 75 μm in diameter. There is an array of associated circuitry around the APD with an area approximately 50 to 200 μm in diameter. The total number of pixels within a total detector area of about 4 cm may be, for example, about 10,000 to 160,000, or with larger detector areas there may be millions of pixels.

In some implementations, TIAs and other support circuitry for a given APD can be turned off or placed in a low power (or “hibernation”) mode to save power. Figure 21 shows an example of circuitry for a detector module. In this example, there is a photodiode 2100 (e.g., APD) that represents one pixel of an on array of photodiodes fabricated on a photonic integrated circuit (PIC). For example, signal processing circuitry 2102, implemented as an analog/mixed signal application specific integrated circuit (ASIC), may include pixel circuitry 2104 for individual pixels, and a pixel selected based on signal validity information. and a controller 2106 (e.g., including a multiplexer or other selection circuitry) capable of selecting received data for processing. Pixel circuitry 2104 includes a TIA, limiting amplifier, and signal detection/automatic gain control circuit module to reduce bit errors, which together enable detection of a data signal. Using pixel circuitry 2104 and controller 2106, signal processing circuitry 2102 is configured to monitor the photocurrent from photodiode 2100 and generate an expected modulated data signal in a predetermined spectral domain (e.g., The TIA and other circuitry can be activated as soon as the current in the spectral domain) exceeds a predetermined threshold. This selective activation reduces the overall power consumption and local heat generation of the detector array.

In some implementations, the electronic array of amplifiers and other circuitry are placed relatively close to the photodetector array to reduce noise and capacitance. Figure 22 shows an example of a detector array 2200 comprising an arrangement of various layers in a compact configuration. APD layer 2202 includes APDs that collect incident light. Middle layer 2204 includes an array of TIAs, gain circuits, and digitizer circuits. Intermediate layer 2204 may be fabricated on the same die as APD layer 2202, for example, or may be connected to a die containing APD layer 2202 using 3D integration. The back layer 2206 includes additional DSP and signal conditioning circuitry so that each pixel can have signal processing capabilities. One or more I/O chips 2208 along one or more edges of the back layer 2206 are used to receive signals from a group of pixels corresponding to a particular received beam. In some examples, individual elements may be shared by multiple pixels. For example, Figure 23 shows an example detector array arrangement where there are multiple APDs for each microlens, each APD having its own TIA, and a single DSP element for multiple neighboring TIAs ( 2300). Various other arrangements are also possible, including arrangements where each pixel has the same set of elements.

Figure 24 shows an example where three different beams are received by detector array 2400. Due to atmospheric effects, vibrations of the platform supporting the receiver-side and/or transmitter-side optical elements, and/or relative movement of nodes (such as a drone communicating with an airplane or telecommunications between two satellites). , the focus spots on detector array 2400 may move. The resulting intensity patterns for movement of focus spots over a given period of time are shown in Figure 24. For example, the faster the platform moves, the faster the focus spot of the beam moves over different pixels. Therefore, to achieve continuous data transmission without lapses, the pixel or pixels responsible for collecting data must be transmitted seamlessly as the focus spot moves. This can be achieved using a circuit consisting of a fast feedback loop that can detect pixels that are receiving a sufficiently high signal and track the movement of the focus spot. In some implementations, the circuitry is also configured to predict the next pixels that should be ready to collect data. This can be implemented, for example, by appropriate control of analog gain circuitry and circuitry in the digital layer coupled to I/O ports 2402 for streaming data associated with different tracked beams. Configured to control the throughput of the array.

An example of an FSO communication system is shown in FIG. 25, including a free-space TX/RX unit 2500 associated with a given local node, and a peer TX/RX unit 2502 associated with a remote node. To achieve optimal signal quality, it is advantageous to lock in the optimal direction for the best signal-to-noise ratio and bit error rate. Accordingly, the optical packages of the receiver and transmitter at the two nodes can be pointed towards each other, ideally with a feedback mechanism to obtain the best transmission direction and best pixel selection for reception. This can be done if the receiver system has power monitor circuitry and potentially error monitoring DSP circuitry. When error correction coding, such as forward error correction (FEC), is used, some of the bits in the transmitted data stream are used to detect error bits. The receiver system can monitor the amount of errors over time and correct their onset angle. The transmitter system may also use the coarse alignment and fine alignment phases of the initial alignment, and dynamic alignment, for example, as described above, based on that feedback to optimize beam positioning on the remote node's detector array. Strength information may be received from a remote node (e.g., via a side-channel link) to steer the transmitted beam.

Figure 26 shows how these alignment techniques can also be used to detect the first light. Before the FSO link is established, both the transmitter and receiver can seek directions to help establish a line-of-sight link. For example, coarse alignment can be performed with a telescope, a GPS location, predetermined position conventions, and/or a temporary optical retroreflector, which can help two nodes establish the coarse alignment.

27A and 27B, if the transmitter uses an optical phased array 2700 as a beam steerer and the receiver-side lens 2702 is adjustable, the beam divergence and field of view help locate the first light. It can be initially set to a wide angular range on detector array 2704 (Figure 27A) and then focused to a narrowed angular range (Figure 27B) for optimal data transmission.

Although the disclosure has been described with respect to specific embodiments, the disclosure is not intended to be limited to the disclosed embodiments, but rather to cover various modifications and equivalent arrangements included within the scope of the appended claims. , it should be understood that its scope is to be given the broadest interpretation to include all such modifications and equivalent structures as permitted under the law.

Claims (20)

A device for optical communication with a remote node, comprising:
a receiver module configured to receive at least a portion of at least one optical beam from the remote node, and
A transmitter module configured to transmit at least one optical beam to the remote node.
Including,
The receiver module:
at least one array of optical detector modules;
(1) an array of optical detector modules, wherein the array of optical detector modules does not exactly coincide with the focal plane of a lens, or (2) a microlens array proximate to the array of optical detector modules, wherein the microlens array is a lens not exactly aligned with the focal plane of - at least one said lens configured to focus light proximate to; and
comprising circuitry configured to control the optical detector modules and provide intensity information based on one or more signals from one or more of the optical detector modules;
The transmitter module:
at least one optical phased array providing the optical beam to be transmitted to the remote node; and
Circuitry configured to receive intensity information from the remote node and control the optical phased array to steer the optical beam transmitted to the remote node based on the intensity information received from the remote node.
Device, including. 2. The device of claim 1, wherein the array of optical detector modules comprises a two-dimensional array of photodiodes each providing a respective photocurrent to a corresponding amplifier. 3. The device of claim 2, wherein the photodiodes include avalanche photodiodes and the amplifiers include transimpedance amplifiers. 3. The method of claim 2, wherein the circuitry of the receiver module configures a subset of amplifiers that are less than all of the amplifiers to be powered on based at least in part on comparing the photocurrent in the corresponding amplifier to a threshold. A device configured to make a decision. 3. The method of claim 2, wherein the circuitry of the receiver module comprises: a first subset of the photodiodes receiving at least a portion of the optical beam, and a second portion of the photodiodes receiving at least a portion of the other optical beam. A device configured to determine a set. The apparatus of claim 1, wherein the receiver module further comprises a light source providing a coherent local oscillator beam for coherently receiving the optical beam. 7. The apparatus of claim 6, wherein the light source provides multiple coherent local oscillator beams, the multiple coherent local oscillator beams for coherently receiving multiple optical beams simultaneously. 2. The transmitter module of claim 1, wherein the intensity information from the remote node is transmitted, at least during setup of the free space optical communication link, via a side-channel network separate from the free space optical communication link with the remote node. Received by the circuitry of the device. 9. The method of claim 8, wherein additional intensity information from the remote node is received by the circuitry of the transmitter module to control the optical phased array via the free space optical communication link after setup of the free space optical communication link. used device. The device of claim 1, wherein the receiver module includes the microlens array. 11. The device of claim 10, wherein the distance between the microlens array and the lens is at least 5% greater or less than the focal length of the lens. The apparatus of claim 1 , wherein the receiver module includes the at least one lens configured to focus light proximate the array of optical detector modules. 13. The device of claim 12, wherein the distance between the array of optical detector modules and the lens is at least 5% greater or less than the focal length of the lens. The device of claim 1 , wherein the array of optical detector modules comprises an array of photodetectors within a photonic integrated circuit. 2. The method of claim 1, wherein the optical phased array comprises a two-dimensional array of optical emitters each coupled to a respective optical phase shifter, and wherein each phase shift signal applied to the optical phase shifters is at least in a first plane. Controlling the steering of the propagation axis of the optical beam transmitted to the remote node. 16. The method of claim 15, wherein each phase shift signal applied to the optical phase shifters controls steering of the propagation axis of the optical beam transmitted to the remote node in a second plane perpendicular to the first plane. Device. 16. The apparatus of claim 15, wherein wavelength tuning of optical waves emitted from the optical emitters controls steering of the propagation axis of the optical beam transmitted to the remote node in a second plane perpendicular to the first plane. . A method for optical communication with a remote node, comprising:
transmitting at least one optical beam to the remote node;
receiving at least a portion of at least one optical beam from the remote node;
providing intensity information based on one or more signals from one or more optical detector modules in an array of optical detector modules that detect the portion of the optical beam received from the remote node;
(1) an array of optical detector modules, wherein the array of optical detector modules does not exactly coincide with the focal plane of a lens, or (2) a microlens array proximate to the array of optical detector modules, wherein the microlens array is a lens focusing light with said lens in close proximity to - not exactly aligned with the focal plane of; and
Controlling at least one optical phased array to steer the optical beam transmitted to the remote node based on intensity information received from the remote node.
Method, including. 19. The method of claim 18, wherein the intensity information from the remote node is transmitted to circuitry of a transmitter module, at least during setup of the free space optical communication link, via a side-channel network separate from the free space optical communication link with the remote node. Received by, method. A device for optical communication with a remote node, comprising:
a receiver module configured to receive at least a portion of at least one optical beam from the remote node, and
A transmitter module configured to transmit at least one optical beam to the remote node.
Including,
The receiver module:
at least one array of optical detector modules;
a microlens array proximate the array of optical detector modules;
at least one lens configured to focus light proximate to the microlens array; and
comprising circuitry configured to control the optical detector modules and provide intensity information based on one or more signals from one or more of the optical detector modules;
The transmitter module:
at least one optical phased array providing the optical beam to be transmitted to the remote node; and
An apparatus comprising circuitry configured to receive intensity information from the remote node and control the optical phased array to steer the optical beam transmitted to the remote node based on the intensity information received from the remote node.

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